Process of reclaiming waste polychloroprenes



Patented Mar. 7, 1944 PROCESS OF RECLAIMING WASTE POLYCHLOROPBENESWalter G. Kirby and Paul M. Elliott, Naugatuolr,

Conn, assignors to United States Rubber Company, New York, N. Y., acorporation or New Jersey No Drawing. Application January 9, 1942,

- Serial No. 426,179

13 Claims. (Cl. 280-23) billzing agents is sold under the name of Neo-'prene in a number of types such as E, M, G, GN, I, etc. Neoprene GN, anoutstanding material, is understood to be prepared by polymerization ofchloroprene in the presence of sulphur. Neoprene I is understood to beprepared by polymerization of chioroprene and a portion of anunsaturated nitrile in the presence of sulphur. When these arious typesof neoprene are mixed with selected modifying agents, softeners,fillers, reinforcing agents, etc., in the manner generally known to theart, and said mixtures are subjected to a heating process, the neoprenemixture is converted from a plastic to a tough elastic material by aprocess generally called curing or vulcanizing. The tough elastic bodyis referred to as vulcanized neoprene. The vulcanization step may occurat low or high temperatures and may proceed to various degrees. If ittakes place at or near room temperature or during processing, it isreferred to as scorching." The neoprene mixtures in which scorching" hasproceededto even a relatively slight degree cannot be satisfactorilymilled, tubed, calendered, or otherwise processed in the industry and somust be scrapped. For convenience scorched and fully vulcanized elasticneoprene mixtures or products made from such mixtures will bereferred'to herein as vulcanized neoprene.

The art of the reclaiming of vulcanized ordinary rubber scrap iswell-known. In .all of the economical methods for reclaiming scraprubber, that are in commercial use today, high temperatures are used.These elevated temperatures which range from approximately 300 F. toapproximately 400 F. are desirable because they accelerate the reversionof vulcanization and speed up the action of so-called softening agents,and thus contribute to economical plasticization. These highertemperatures are also desirable to accelerate and promote the rapiddestruction of fibre where it is present. Because of these facts,equipment that will accommodate these higher temperatures has becomestandardized and is now in use throughout the rubber reclaimingindustry.

does not combine with sulphur to bring about vulcanization and does notundergo reversion of vulcanization through the medium of heat, to changeit from an elastic to a plastic form. On the contrary when heat andespecially the higher temperatures referred to are applied to vulcanizedneoprene it becomes harder and is said to be further vulcanized.Therefore, one of the great difilcultles in attempting to reclaim scrapvulcanized neoprene is the fact that as the temperature is raised duringthe process to accelerate the action of oils and softening agents inplasticizing or otherwise breaking down the polymer to a p1astic state,there occurs during the same period a gradual further polymerizing andhardening of the neoprene, due to these temperatures, which counteractsany plasticizing'effect accomplished.

For this reason, processes that have been recommended to date forreclaiming scrap vulcanized neoprene have been limited to lowtemperatures. At low temperatures it is diflicultto get sufiicientsoftening action from softening agents, without using preiudicallyexcessive amounts.

Since high temperatures will soften ordinary vulcanized rubber scrap andwill harden vulcanized neoprene scrap it is apparent that the usualrubber reclaiming methods such as the high temperature digester alkalior digesterzinc chloride processes or the high temperature heater"process cannot be used to reclaim combinations or mixtures of thesescraps. This fact has been a source of considerable concern among scraprubber reclaimers because the introduction of neoprene into rubberarticles such as for example an automobile tire having a neoprene treadand a rubber carcass ora rubber gasoline hose having a neoprene innerlining would cause this type scrap to become valueless for furtherreclaimlng use. Also the accidental mixing of neoprene scrap with rubberscrap would destroy the reclaiming value of otherwise high qualityvulcanized rubber scrap.

An object of this invention is th provide through the aid of certainreclaiming agents a method of reclaiming scrap vulcanized neoprene athigh er temperatures. Another object is to provide a process forreclaiming at one time and in the same vessel mixtures of scrapvulcanized rubber and scrap vulcanized neoprene, as well as to reclaimscrap containing combinations of rubber and neoprene. A further objectis to provide a method of reclaiming vulcanizedneoprene that will allowuse of the same equipment that is regularly used for reclaiming rubber,thus permitting present Neoprene is different from rubber in that itestablished rubber reclaiming plants to reclaim or an'aiiphatichydrocarbon group of from 1 to 18 carbon atoms, will permit reclaimingof scrap vulcanized neoprene by heating the said scrap in a suitablestate of sub-division with selected amounts of the reclaiming agent, andoptionally with suitable oils, swelling and/or binding agents. Where Ris an aliphatic hydrocarbon group it may be further substituted by otherradicals such as hydroxy, alkoxy, aldehyde, keto, or carbonyl.

Examples of these reclaiming agents include formic acid, acetic acid,propionic acid, butyric acid, lauric acid, myristic acid, carbonic acid(or equivalently water and carbon dioxide) palmitic acid, stearic acid,isobutyric acid, oleic acid, linoleic acid, llnolenic acid, ricinoleicacid, abietic acid, rosin acids, oxalic acid, malonic acid, succinicacid, glutaric acid, adipic acid, sebacic acid. slycollic acid, lacticacid, tartaric acid, malic acid, citric acid, acrylic acid, crotonicacid, vinylacetic acid, maleic acid, acetoacetic acid, gluconic acid,pyruvic acid, et cetera; the above named materials are mentioned merelyas examples of the type of compound that can be employed, and theinvention is not to be understood as limited to these examples.

The proportion by weight or our reclaiming agents based on the scrapneoprene may vary depending on their strength, cost and nature of theend product of reclamation desired. Generally from 2 percent to 20percent by weight of the reclaiming agent may be used. Preferred amountsbased on one 01 the agents such as acetic acid may range from 5 topercent.

The following examples are given in illustration of the invention:

Example 1 Scrap vulcanized neoprene is reduced to a desired particlesize and placed in an autoclave type vessel commonly known in the rubberreclaiming industry as a digester. The scrap, together with softeningoils, water, and our reclaiming agent, is sealed in the digester andheated under pressure. An illustrative batch is as follows:

Pounds Scrap vulcanized neoprene 10,000 Pine oil fraction 1,000 Rosinoil 1,000 Our reclaiming agent Variable Water 20,000

The heating time varies depending on the type of scrap and thetemperature used, and preferably ranges frcm three to thirty hours. Thetemperature usually ranges between about 300 F. and abo t 420 F. Thecharge is then washed and drie following the usual procedure employedfor reclaiming rubber, and it is then ready to be refined and furtherprepared in the mill room for shipment. The -ilnal product is fullyreclaimed and has a quality comparable to new compounded neoprene.

Example 2 Another procedure is to reduce the scrap vulcanised neopreneto a desired particle size, then place it in an autoclave type vessel,commonly known in the reclaiming industry as a "heater" ordevulcanizer." This process differs from the digester process in thatthere is usually no agitation and there is practically no water present.The charge under treatment is in a semi-moist state rather thansuspended in a solution. The following batch is illustrative:

- Pounds Scrap vulcanized neoprene----------- 3,000 Pine oil traction300 Rosin oil This charge is then sealed in the "heater" and so no Pinei l irsctlon. Ros oil period of treatment and temperature used will varywith the type of scrap, and the period of time and temperature may be asabove speciiied. The product after the usual milling is fully reclaimedand of a quality comparable to new compounded neoprene.

In order to further illustrate this invention we give thefollowing-examples using the previously mentioned digester typeequipment.

Ex. Ex. Ex. 8 i b 0 7 Scrap vulcanized Lact Bebacic acid Viscosity oftreated roduct as shown y a Mooney shearing plastomotcr........

Each of the above were treated by loading the charge into a digester andheating with steam for about 16 hours at a temperature of about 365 F.

The eflectiveness of a reclaiming operation in recovering scrapvulcanized neoprene may be quantitatively shown by means of aninstrument widely used for this purpose in the reclaim rubber industry,namely, the Mooney shearing disc plastometer. This device has beendescribed by M. Mooney in Industrial 8: Engineering Chemistry, an. ed.6, 147 (1934). By means of this device the viscosity of a plasticmaterial in shear may be readily and quantitatively measured. Experiencehas shown that materials with a Mooney viscosity of 50 to when tested atF. can be readily and eiiiciently processed on standard rubber workingmachinery, but that materials of a very high viscosity such as 200 andover when tested at 180 F. cannot be so treated.

Example 3 represents a charge in which none of our reclaiming agents areused. The product has a viscosity of and is considered too hard to mill.Examples 4, 5, 6, 7, 8 and 9 represent charges using certain of ourreclaiming agents and show that these agents have a definite reclaimingaction. In these examples the viscosities range from 17 to 35 and theproducts can be easily milled and made useful to the rubber trade. Inthose examples wherein the viscosity is below 50, the reclaimingoperation would normally be modified by using less 011. less reclaimingagent, or shorter heating time. or a combination of these changes togive a viscosity in the preferred ranae. Proper adjustment could easilybe made by one experienced assasss in the art to give a product of thedesired plasticity.

Very similar reclaiming action will result from our reclaiming agents ifused in a "heater" instead of a digester. The treatment in a heaterwould be carried out the same as the treatment in a digester except thatpercent of water based on the weight of the scrap would be used insteadof 200 percent,

Although for purposes of comparison, our reclaiming agents are used inthe above examples with 10 parts of pine oil fraction,- and 10 parts ofrosin oil, to 100 parts of scrap vulcanized neoprene, it is to beunderstood that our invention is in no way limited to the use of ourreclaiming agents with these oils or proportions of oils. We can use ourreclaiming agents both with and without oils, etc.; and the proportionsand nature of the ofls, swelling agents, penetrants, etc.. used with ouragents may be varied at will to suit the purposes for which the finalreclaimed product isintended. Our agents can further be used withvulcanized neoprene containing all the modifying agents and compoundingagents used in the trade in the production of vulcanized neopreneproducts. For example, magnesia zinc oxide, other metallic oxides,antioxidants, sulphur, accelerators, retarders, and other ingredientswhich eifect the plasticity, rate of cure and/or physical properties ofthe vulcanizate; also softeners, fillers and/or reinforcing materialsmay be used,

The mode of addition of our reclaiming agents is not limited in any wayto the foregoing examples. We may add them at any point in the processand they may be added in any desired form, as for example, as a gas orvapor, or as a solid, or a liquid, or in solution in water or organicsolvents, or in the oils, softeners, etc., which may also be used in theprocess.

It is evident from the above that many variations and embodiments of ourinvention may be made without departing from the spirit or scopethereof.

Having thus described our invention, what we claim and desire to protectby Letters Patent is:

' 1. A process of reclaiming scrap containing vulcanized polychloroprenewhich comprises heating the same while in a sub-divided condition at atemperature from about 300 F. to

about 420 F. in the presence of an acid of the formula R-COOH, where Ris selected from the group consisting of H, OH, COOH and aliphatichydrocarbon groups containing from 1 to 18 carbon atoms.

2. A process of reclaiming scrap containing vulcanized polychloroprenewhich comprises heating the same while in a sub-divided condition at atemperature from about 300 F. to about 420 F. in the presence of analiphatic acid having from 1 to 18 carbon atoms.

3. A process of reclaiming scrap containing vulcanized polychloroprenewhich comprises heating the same while in a sub-divided condition at atemperature from about 300' I". to about 420 F. in the presence of anadded amount of a fatty acid having from 1 to 18 carbon atoms in theopen chain.

4. A process of reclaiming scrap containins vulcanized polychloroprenewhich comprises heating the same while in a sub-divided condition at atemperature from about 300' I". to about 420' 1". in the presence ofoleic acid.

5. A process of reclaiming scrap containing elastic polychloroprenewhich comprises incorporating therein an acid of the formula R-COOH,where R is selected from the group consisting of H, OH, COOH andaliphatic hydrocarbon groups containing from 1 to 18 carbon atoms, andheating the same while in a subdivided condition at a temperature fromabout 300 F. to about 420 F. for a time sufli ient to reduce the elasticpolychloroprene to a astic state where it'has a Mooney viscositysubstantially less than 200 when tested at 180 F.

8. A process of reclaiming scrap containing elastic polychloroprenewhich comprises incorporating therein an acid of the formula R-COOH,where R. is selected from the group consisting of H, OH, C001! andaliphatic hydrocarbon groups containing from 1 to 18 carbon atoms, andheating the same while in a sub-divided condition for a time sufficientto reduce the elastic polychloroprene to a plastic state where it has aMooney viscosity substantially less than 200 when tested at 1".

9. A process of reclaiming scrap containing elastic polychloroprenewhich comprises incorporating therein an aliphatic acid having from 1 to18 carbon atoms and heating the same while in a subdivided condition fora time sufiicient to reduce the elastic polychloroprene to a plasticstate where it has a Mooney viscosity of substantially less than 200when tested at 180 F.

10. A process of reclaiming scrap containing elastic polychloroprenewhich comprises incorporating therein a fatty acid having from 1 to 18carbon atoms and heating the same while in a subdivided condition for atime suiiicient to reduce the elastic polychloroprene to a plastic statewhere it has a Mooney viscosity of substantially less than 200 whentested at 180 F.

11. A process of reclaiming scrap containin elastic polychloroprenewhich comprises incorporating therein oleic acid and heating the samewhile in a subdivided condition for a time sufflcient to reduce theelastic polychloroprene to a plastic state where it has a Mooneyviscosity of substantially less than 200 when tested at 180 F.

12. A process of reclaiming scrap containing elastic polychloroprenewhich comprises incorporating therein oxalic acid and heating the samewhile in a subdivided condition for a time suflicient to reduce theelastic polychloroprene to a plastic state where it has a Mooneyviscosity ofosubstantially less than 200 when tested at 18 F.

13. A process of reclaiming scrap containing elastic polychloroprenewhich comprises incorporating therein lactic acid and heating the somewhile in a sub-divided condition for a time sumcient to reduce theelastic polychloroprene to a plastic state where it has a Mooneyviscosity of substantially less than 200 when tested 'WALTER G. KIRBY.PAUL M. HHO'I'I'.

